Generation and modulation of alternating current signals



May 3, 1949.

Filed Nov. 29, 1944 A. GOLDBERG 2,469,264 GENERATION AND MODULATION OF ALTERNATING CURRENT SIGNALS 2 Sheets-Sheet l Z7 AM/ l/F/f? [OI l; za ,1;

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GENERATION AND MODULATION OF ALTERNATING CURRENT SIGNALS Filed Nov. 29, 1944 2 Sheets-Sheet 2 Y +aoov INVENTOR.

ITTOE/Yi'y STD.

Patented May 3, 1949 UNITED TENT OFFICE GENERATION AND MGDULATION OF ALTEENATXNG CURRENT SIGNALS of Delaware Application November 29, 1944, Serial No. 565,695

3 Claims.

This invention relates to the generation and modulation of alternating current signals. It provides a stabilized generator which operates in response to an applied unidirectional voltage to deliver an alternating current signal of an amplitude which is proportional to the amplitude of the appliedunidirectional voltage. It'also provides mcdulating means whereby this generated alternating current signal may be combined with separate unidirectional voltages to produce alternating voltages, each *of which is proportional .to the product of the generated alternating current signal and a different one of the separate unidirectional voltages.

The illustrated form of the invention includes a high gain feedback amplifier which receives its input from a tuning fork and delivers at its output the generated alternating current signal. Connected between the output of the feedback amp-lifier and the tuning fork are: (1) a transformer, (2) a rectifier, (.3) a direct current amplifier which functions to deliver a unidirectional voltage proportional to the difference between the amplitudes of the rectified voltage and that of the unidirectional voltage which determines the amplitude of the generated alternating current signal, (4) a modulator which responds to both the output of the feedback amplifier and the 'out put of the direct current amplifier, and (5) an alternating current amplifier through which the tuning fork is excited from the modulator.

The tuning fork obviously may be replaced by any other suitable type of generator. While it is illustrated as provided with electrostatic pickups through which it is coupled to the feedback amplifier, it is apparent that these pickups may be replaced by magnetic pickups or the like.

Among the objects of the invention are to provide a stabilized generator which functions to deliver an alternating current signal of an amplitude which is proportional to that of a controlling unidirectional voltage: to provide a modulator which functions in response to an alternating current signaland a unidirectional voltage to deliver an alternating signal which is propoi tional to the product of such signal and voltage: and to provide an improved means and method of operation whereby there is made available both a generated alternating current signal of an amplitude proportional to that of a un. irectional control voltage, and one or more auxiliary a1ternating current signals, each of an amplitude proportional to the product of the generated altermating current signal and a different one of such unidirectional control voltages.

The invention will be better understood from 2 the following description, considered in connection with the accompanying drawings, and its scope is indicated by the appended claims.

Figure l of the drawings is a schematic showing of the improved, stabilized signal generator and modulator, and

Figure 2 is a wiring diagram of the stabilized signal generating part of Figure 1.

In connection with these figures, it should :be understood that the feedback amplifiers which perform the modulating functions are similar to te feedback amplifier which performs the signal generating function. For this reason, only the pickups to which the modulator feedback amplifiers are connected are shown in Figure 2.

The apparatus of Figure J. includes a feedback amplifier it, which receives its input from a tuning fork i I through a pickup coupling l2 and delivers its output through leads 'l3-M. -:Connected to the leads l3i l are the output terminals i5il3, a transformer ll and one input circuit of the modulator 52 (Fig. 2) of a modulater-amplifier unit it. The transformer illiis connected through a rectifier l9 and adirect current amplifier 2% to another input :circuit of :the unit it and the output of this unit is applied to the driving coil 2! of the tuning fork l l.

Applied to the terminal 22 is a unidirectional voltage of an amplitude which determines the amplitude of the alternating signal delivered at the output of the amplifier Ill. Applied through a resistor 23 to the pickup feeding the input of the amplifier ill is a voltage which determines the amplitude of the vibration of the tuning fork M, as hereinafter explained.

The input of a second feedback amplifier '25 is coupled through a pickup 24 to the tuning fork i l. The pickup M is connected through a resistor 52% to a source of unidirectional potential. The output delivered at the terminals 2? and 28 is an alternating voltage which has the same frequency as the tuning fork I I, and has an amplitude ,proportional to the product of the unidirectional voltages applied through the terminal 22 and through the resistor '26 and inversely proportional to the voltage applied through the terminal 53.

Additional pickups 29 and'tll maybe provided to cooperate with other amplifiers in the same way that the pickup 2t cooperates with the amplifier 25.

In the wiring diagram of Fig. 2, 'the feedback amplifier it is shown as consisting of four stages iii, 32, 3,3 and 34. The first stage 3| is coupled to the tuning fork H through the pickup l2 and the last stage is connected to thefprimaiy *winding of the transformer H. The secondarywind- 3 in of the transformer l1 delivers its output to the rectifier l9. The rectified voltage available at the output terminals of the rectifier is smoothed or filtered by a network 35 and applied to one control grid 36 of the direct current amplifier 28.

To the other control grid 31 of the direct current amplifier 20 is applied a bias potential determined by the potential drop of resistors 38 and 39. These resistors are connected between a lead 40 maintained at a positive potential of 300 volts and a lead 4! maintained at a negative potential of 300 volts. The potential developed across these resistors corresponds to the potential applied to the terminal 22 of Fig, 1 and is set at any desired value by suitable adjustment of the resistor 39.

The modulator 42, which forms part of the modulator-amplifier I8 of Fig, 1, is provided with two control grids 43 and 44. The potential of the grid 44 is determined by the potential drop of a resistor 45 connected in the right-hand plate circuit of the direct current amplifier 28. Since the potential drop of the resistor 45 is responsive to the potential of the grid 36, and this grid potential is determined by the output of the rectifier, it follows that the potential of the grid 44 is varied in accordance with the amplitude of the rectified voltage.

The left-hand plate circuit of the amplifier 28 is connected to a gaseous voltage regulator tube 51 which receives its operating current through the resistor 45. The negative electrode of the regulator tube 51 is connected to the negative terminal of the 300 volt power supply. Also connected to the positive electrode of the regulator tube 51 is the cathode of the modulator tube 42. The D. 0. potential of the second control grid of the modulator tube 42 is maintained at the cathode potential due to the D. 0, return through the choke 45. Thus the regulator tube 51 maintains the left hand plate of the tube 28, the oathode of the modulator tube 42, and the second control grid of the modulator tube 42 at a fixed D. C. potential of +150 volts with respect to the negative terminal of the 300 volt power supply. There is applied to the grid 43 through a capacitor 4?, a resistor 48 and an output lead 49 of the feedback amplifier 3l-3233-34 a part of the alternating current signal delivered by this feedback amplifier. With proper adjustments in the various parts of the circuit, the grids 43 and 44 function to make available at the output terminals of the modulator 42 alternating current of an amplitude which responds very closely to the potential drop of the resistors 38 and 39. Thus, the rectified unidirectional voltage is constantly compared with voltage drop of the resistors 38 and 39, so that the amplitude of the alternating current signal is stabilized at a value determined by the potential drop of these resistors.

The stabilized alternating current output of the modulator 42 is amplified by the amplifier 58 and supplied through leads I52 to the driving coil 2| of the tuning fork l I.

Potential (corresponding to that applied through the resistor 23 of Fig. 1) is applied through a lead 53, a potentiometer 54, and a resistor 23 to the pickup feeding the input of the amplifier 3l32-3334. As previously indicated, adjustment of this potential determines the amplitude of the vibration of the tuning fork. Such adjustment is made by means of the potentiometer 54.

I The gain of the loop, formed as outlined above, is determined by adjustment of a potentiometer 4 55 through which the modulator 42 is coupled to the amplifier 50.

The operation of the signal generator is readily understood, if it be assumed that the tuning fork H is vibrating and a unidirectional voltage is applied to the terminal 22 of Fig. 1, or across the resistors 38 and 39 of Fig. 2, and a unidirectional voltage is also applied to pickup l2 through resistor '23. Under these conditions, an alternating voltage of the fork frequency is applied to the input circuit of the feedback amplifier 31- 32--33-34 (indicated by the reference numeral l0 in Fig. 1), The output voltage of this amplifier is stepped up by the transformer I1, is rectified, and is compared with the unidirectional voltage across the resistors 38-39. The difference between these unidirectional voltages is utilized to control the gain of the modulator 42 which is excited by alternating potential applied from the output of the amplifier"3l-3233-34 through the leads 49 to the grid'43. The modulator output is amplified and utilized to drive the tuning fork. Thus, the system operates so that the rectified voltage is always maintained very close to the voltage across the resistors 38 and 39.

How this result is achieved may appear more clearly from the theoretical considerations outlined below. In these considerations, the various reference characters are identified as follows:

A=the fork amplitude of vibration,

B=the value of the voltage applied to pickup l2 through the potentiometer 54, and resistor 23,

C=the value of the voltage across resistors 38 and 39,

Eo1=alternating voltage at output of amplifier 3l-323334 (amp. ill in Fig. 1),

Eon=alternating voltage at output of amplifier 25 (Fig. 1),

D=unidirectional voltage applied to pickup 24 through resistor 26,

Gm=gain of amplifier [0 (Fig, 1),

Gn=gain of amplifier 25,

Em=alternating voltage output of 42 (Fig. 2),

101,762, k3, etc.=constants,

For the sake of simplicity, it is assumed that the modulator 42, the tuning fork drive, etc. are linear. This, of course, is not essential to the operation of the system. It is apparent that the following relations are established:

EoI=k1ABGm (1) A=lczEm (2) Em=k3Eo1(C E0DC) (3) EoDo=k4EoI (4:) Em=k3EoI(Ck4EoI) (5) EoI=k1k2EmBGm (6) Eol=7fi1k2BGmk3EoI(C'-k4EoI) (7) k Ic k BCG 1 nannies...

If kikzkaBcGm is large relative to 1 (meaning only that the loop gain is high), the 1 may be neglected and there results for practical purposes:

This last equation shows that the output voltage EoI of the generator feedback amplifier 3l323334 is proportiona1 to the voltage drop across the resistors38 and 39. This shows that the voltage of the alternating current signal output is controlled by the voltag drop across the resistors 38 and 39.

From Equations 1 and 8 it is seen that:

E.1=k.ABG..= 4

From Equation 10 it is apparent that the amplitude of the vibration of the fork II is inversely proportional to the unidirectional voltage applied through the potentiometer 54, and resistor 2-3. It is, therefore, possible to control the fork amplitude by adjustment of this potentiometer without affecting the generator alternating output voltage EoI.

In the operation of the system, the voltage drop of the resistors 38 and 39 is adjusted first to give the desired signal generator output voltage. The voltage applied through the potentiometer 54 and resistor 23 is then adjusted to give the proper vibration amplitude of the tuning fork.

If a unidirectional voltage is applied to the pickup connected to the input of the modulator feedback amplifier (Fig. 1) through the resistor 26, there is made available at the output terminals of this amplifier an alternating voltage EoII, which has the same frequency as the tuning fork and has an amplitude proportional to the product of this unidirectional voltage and the amplitude of the vibration of the tuning fork.

EoII=K1ADGn (11) There is thus made available a linear modulator having an alternating current output which is proportional to a unidirectional voltage. This tional voltages are each to modulate the same I alternating current signal. The phase of the output voltage of the linear modulator is a constant, or a constant plus 180 with respect to the output voltage of the signal generator. The constant depends upon the relative phase shifts through amplifiers l0 and 25 of Fig. 1, and the phase may .be shifted 180 by reversing the polarity of the unidirectional voltage applied through resistor 25 with respect to the unidirectional voltage applied through resistor 23 of Fig. 1.

I claim as my invention:

1. The combination of alternating current supply means having input and output circuits, modulating means having a pair of control grids, an alternating current amplifier having its input connected to the output circuit of said supply means and having an output circuit, means for applying a fixed unidirectional potential, means connected to said amplifier output circuit and responsive to said fixed unidirectional potential for applying to one of said modulator grids a potential representative of the difi'erence between said fixed unidirectional potential and the amplitude of the output potential of said amplifier, means for applying the output potential of said amplifier to the other of said modulator grids, and means for applying the output potential of said modulator to the input circuit of said supply means.

2. The combination of alternating current supply means having input and output circuits, modulating means having a pair of control grids, an alternating current amplifier having its input connected to the output circuit of said supply means and having an output circuit, means for applying a fixed unidirectional potential, means connected to said amplifier output circuit and responsive to said fixed unidirectional potential for applying to one of said modulator grids a potential representative of the difference between said fixed unidirectional potential and the amplitude of the output potential of said amplifier, means for applying the output potential of said amplifier to the other of said modulator grids, means for applying the output potential of said modulator to the input circuit of said supply means, means for adjusting the value of said fixed potential, and means for stabilizing said fixed potential at such adjusted value.

3. The combination of alternating current supply means having input and output circuits, alternating current rectifying means, an alternating current amplifier connected between said rectifying means and the output circuit of said supply means, a modulator having first and second control grids and an output circuit including a cathode and an anode, a direct current am- .plifier including first and second anodes and first and second control grids, means connecting the output of said rectifying means to the first of said direct current amplifier grids, means for applying a fixed potential to the second of said direct current amplifier grids, means connecting the first of said direct current amplifier anodes to the first of said modulator grids, means for stabilizing the cathode of said modulator and the second anode of said direct current amplifier at the same voltage, means for applying the output potential of said alternating current amplifier to the second of said modulator grids, and means connecting the output circuit of said modulator to the input circuit of said supply means.

EDWIN A. GOLDBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,869,331 Ballantine July 26, 1932 2,103,619 Hallmark Dec. 28, 1937 2,138,138 Bruckner Nov. 29, 1938 2,283,241 Van Cott May 19, 1942 2,292,790 Millar Aug. 11, 1942 2,294,171 George Aug. 25, 1942 Certificate of Correction Patent N 0. 2,469,264 May 3, 1949 EDWIN A. GOLDBERG It is hereby certified that error appears in the printed specification of the above numbered patent requiring correetion as follows:

Column 6, list of references cited, under the heading United States Patents, add the following THOMAS F. MURPHY,

Assistant Uommz'ssz'oner of Patents. 

